Peptidyl argininal (arginine aldehyde) transition-state analog inhibitors of trypsin-like serine proteinases will be synthesized and utilized to study the role of selected proteinase enzymes and proteinase containing pathways in B16 melanoma cell metastasis in mice. A specificity index will first be developed from the ratios of peptidyl argininal inhibition constants obtained in vitro against targeted proteinases. The targeted proteinases will include proteinases of both the thrombolytic and fibrinolytic pathways, and plasminogen activator secreted by the highly metastatci F10 B16 melanoma cells. The peptidyl argininals will contain sequences selected to give orders of magnitude differences in KI towards a particular proteinase. Melanoma cells will be introduced into C57BL/6 mice treated with specific doses of peptidyl aldehyde proteinase inhibitors of varied amino acid sequences. The concentration dependence of peptidyl aldehyde inhibition of the formation of metastatic melanoma colonies in the lungs will be determined. Two methods of melanoma cell injection will model initial and later stages of the metastatic process. From a comparison of the concentration dependence of metastatic inhibition in vivo to the specificity indices created against the targeted proteinases in vitro the role of specific proteinases and proteolytic pathways in the different stages of metastasis will be determined, as well as the sensitivity of metastases towards inhibition by different amino acid aldehyde sequences. The peptide aldehyde leupeptin is non-toxic in animal experiments in which the inhibition of selective proteinases occurs. Thus these selective and potent transition-state analog proteinase inhibitors can form the structural basis of compounds useful for the inhibitors of metastases and tumor cell invasiveness in humans, as well as to serve to elucidate important features in the mechanism of cancer cell metastasis.